1. Field of the Invention
The present invention is directed to a computed tomography apparatus operable in a spiral scanning mode for obtaining an image of a patient's heart, as well as to a method for operating such a computed tomography apparatus for obtaining cardiac images.
2. Description of the Prior Art
It is known to conduct helical or spiral scanning of a patient, using a computed tomography apparatus, by causing the measurement unit consisting of the X-ray source and the detector to continuously rotate while displacing the patient bed along its longitudinal direction (z-direction). From the detector data, volume data of the subject of examination can be obtained using an image computer.
Movements of the organs, in particular of the heart, can lead to motion artifacts in the image produced from the volume data, due to the relatively long scan time.
U.S. Pat. No. 4,182,311 describes a method for computed tomography of the heart which does not make use of spiral scanning. In parallel with the scanning of the heart, the ECG signal is recorded. On the basis of the ECG signal, those projections are selected that correspond to a particular phase of the heart action. These projections, associated with various projection angles, are combined to form a dataset that allows the reconstruction of an image.
In U.S. Pat. No. 5,383,231 a method is described for spiral scanning of the heart by means of a computed tomography apparatus, in which, in a manner analogous to the method of U.S. Pat. No. 4,182,311, projections associated with various projection angles and/or various revolutions of the measurement system, and which reproduce the same phase of the heart action, are combined to form datasets that allow the reconstruction of CT images, in particular three-dimensional CT images.
In both cases, an improvement is achieved in comparison to tomographic examinations of the heart that take place without taking into account the ECG signal; however, sufficiently sharp images still are not produced.